Unsolvable Woofer Pumping (Phono only)

Discussion in 'Audio Hardware' started by branden_8091, Dec 3, 2019.

  1. branden_8091

    branden_8091 New Member Thread Starter

    Location:
    Ontario, Canada
    I'm at a loss for trying to find the source of my "woofer pumping." It's most noteworthy when playing something that is mostly/all treble, and the woofers of my Focal Aria 906s are going nuts (inaudibly, of course). Turntable is a Debut Carbon with Ortofon 2M Blue.

    Initially I was told it's an isolation problem, so I better isolated my TT, even put it right on the concrete floor to test! Next I thought maybe a problem with the TT itself, so tried a couple others, no change. So I figured it must be acoustic feedback, as with the TT stopped and stylus on a record, I could produce woofer pumping by tapping on certain parts of my stand...but it is also not this! I turned off my amplifier and recorded from the pre-out to a Tascam digital recorder and played that back afterwards and the pumping STILL happened! So I tried an Schiit Mani phono stage, no change in woofer pumping...I was sure it had to be my pre-amp...

    So a local audiophile came over with a couple of pre-amps and we tried those. The only time the problem went away was when the subsonic filter that one had was engaged. So, I've ordered some Harrison Labs "FMODs" (20Hz high pass) to see if they will help. If they do, I may order a KAB RF1 one day...but don't want to spend that much if I don't have to.

    Any other ideas on what could cause this?!

    tl;dr: Woofer pumping not caused by isolation, acoustic feedback, phono/preamp or a compliance issue...what's happening?!
     
  2. StimpyWan

    StimpyWan Forum Resident

    It sounds as if you need an old-school preamp or EQ (look for Audio Control), with a built in subsonic filter. Preamp's used to have that feature, to roll off turntable rumble. Maybe it'll start showing up again, with the resurgence of vinyl?

    Kenwood Basic C-2 Preamp

    [​IMG]
     
  3. 389 Tripower

    389 Tripower Forum Resident

    Location:
    Moline, IL USA
    If all else fails - I recommend the KAB filter.

    However - once I stopped using ported speakers the problem virtually disappeared for me.

    I do still keep the KAB filter in my tape monitor loop, for when i want to crank up LP’s to very loud levels - to ensure no power is wasted to subsonics.
     
    The FRiNgE and snorker like this.
  4. BIGGER Dave

    BIGGER Dave Forum Resident

    Growing up with vinyl, I always thought it was just something that you accepted. Never thought it was something that needed to be addressed. It happened with my stereo, my neighbor’s stereo, and just anyone I knew with a good quality system. Then one day I was at the local Tweeter Etc (a defunct stereo chain). They demoed an Audio Control D-10 equalizer for me. It included an 18 dB/octave @ 20 Hz Subsonic Filter. They activated the filter while a record was playing and the woofer flapping stopped during the lead-in groove. I thought, “that’s cool, I’ll take it!” But beyond that, always thought it was normal.
     
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  5. branden_8091

    branden_8091 New Member Thread Starter

    Location:
    Ontario, Canada
    I tried something very similar today, actually! It worked just fine...was just borrowed from a local audiophile. I just feel as though this is a band-aid. But maybe not :)
     
  6. branden_8091

    branden_8091 New Member Thread Starter

    Location:
    Ontario, Canada
    Fair enough! I plan on upgrading in the coming year...maybe I'll pick a non-ported speaker :)
     
  7. branden_8091

    branden_8091 New Member Thread Starter

    Location:
    Ontario, Canada
    Glad to hear it's normal. I spent 10 minutes on the phone with my local hifi shop about my issue. Maybe I didn't describe it properly to them.
     
    The FRiNgE likes this.
  8. Jerry James

    Jerry James Rorum Fesident

    I've had this issue on a few occasions with different equipment (even the equipment operating without issue, then changed rooms and the problem arose...). A KAB RF1 filter and all is good ever after amen.
     
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  9. StimpyWan

    StimpyWan Forum Resident

    A bass reflex , ported speaker, looses woofer control, when driven below resonance frequency. And subsonic rumble is definitely below resonance of most woofers. So, that's why you see more rumble induced cone movement in a ported speaker, compared to a sealed, acoustic suspension design.
     
  10. branden_8091

    branden_8091 New Member Thread Starter

    Location:
    Ontario, Canada
    Suddenly this is all starting to make sense. Thank you!!
     
    StimpyWan likes this.
  11. Josquin des Prez

    Josquin des Prez Forum Resident

    Location:
    Midwest USA
    Subsonic filter are bad-aides hiding the real problem, which is very likely an issue with turntable isolation. I've been down this road. I tried the KAB and it just masked the problem a little bit without solving it at all, and diminished the sound quality. I had to do two things to finally solve the problem, once and for all. One was to change from a tonearm that use magnetic bearings and was too finicky to one with mechanical bearings. The other was to get the turntable on a decent isolation platform. Now I can play any records as loud as I want and I get no woofer pumping whatsoever, not even a little bit. No rumble filter necessary. I am using both a pair of ported tower speakers and two sealed subs (with active/passive radiators).
     
  12. The FRiNgE

    The FRiNgE Forum Resident

    Yes! subsonic "warp" frequency is normal with records. This is why all older pre-amps- receivers had a subsonic filter. Most filters have two settings, 10Hz or 20Hz, at 12dB/oct.

    This is not an isolation problem, since you provided sufficient information. The fact the digital recording (if you had the speakers at low volume) produced the same subsonics, rules out feedback/ isolation problems. Subsonic feedback sounds like a "flutter", periodic and regular and can clip the amp and modulate the music. Normal subsonic is more random movement of the woofer, and almost never affects the rest of the audio spectrum. Even though the woofer makes some high sub-sonic excursions, I have never heard of blowing a woofer because of it.

    The subsonic filter is not a "band aid". It is as normal as the RIAA curve in playing our LP's.
     
  13. branden_8091

    branden_8091 New Member Thread Starter

    Location:
    Ontario, Canada
    Thanks a lot! You guys have all made me feel better about this. And yes, for the digital recording I had the speakers right off.
     
  14. Ghostworld

    Ghostworld Forum Resident

    Location:
    US
    Ports always seemed like a compromise.
     
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  15. Thomas_A

    Thomas_A Forum Resident

    Location:
    Uppsala, Sweden
    What is the fundamental tonearm/cartridge resonance frequency? The higher frequency the less problem you will see with woofer.
     
  16. Sterling1

    Sterling1 Forum Resident

    Location:
    Louisville, KY
    A crossover set too high on mains to sub, for example 80Hz rather than 60HZ, can cause pumping, because, using my example, neither sub or mains is producing frequencies between 80 and 60Hz; thus the effect is the pumping sound you hear. Anything else which can eliminate a part of the low end frequency spectrum can also cause the pumping effect, i.e. a cartridge, equalizer, tracking force, or a bad LP among others. The other big thing which causes pumping on LP material is application of gain to extract bass which is not there in the first place.
     
    Last edited: Dec 4, 2019 at 5:53 AM
    branden_8091 likes this.
  17. chervokas

    chervokas Forum Resident

    A subsonic filter is a Band-aid of sorts. It treats the symptom, not the disease.

    Uncontrolled, severe subsonic ringing of the arm/cart that is touched off by any kind of record movement, not just by severe warps, sufficient to drive your speakers into woofer pumping, is mechanical problem relating to the turntable, arm and cartridge. You're not solving the mechanical problem by slapping an electronic subsonic filter into the signal chain. The uncontrolled mechanical resonance is still uncontrolled, still ringing, and maybe even still having an impact on frequencies in the audible range (sometimes you can seen not just the woofers pumping but the arm/cart oscillating). You're just blocking the electronic signal generated by the mechanical ringing from getting past the phono stage. That's fine, it works OK, it's common. But it still leaves unaddressed the core problem. The problems is a turntable/tonearm/cart mechanical one.

    Solutions might include eliminating or minimizing things like motor vibration breakthrough and/or platter bearing rumble (better motor isolation, better motor, different motor control scheme, check the phase split cap if it's an AC synchronous motor; relube main bearing, etc.) Second, you might try a less compliant cartridge so that you have an an arm/cart mass-compliance resonant frequency that higher -- more like in the 13-15 Hz range instead of the commonly cited 8-10 Hz range. Third, and I don't know that this is an add-on option for your current record player, but if there's an aftermarket way to add fluid damping, you might that -- in a tonearm with fluid damping, the fluid damping works like of like a mechanical subsonic filter, controlling the mechanical subsonic resonance.

    The mass-compliance system of any tonearm/cart combo is going to have a subsonic resonance. The trick is to minimize the degree to which it is really kicked into ringing by just playing an unwarped record, and mechanically controlling the ringing so its less long and less substantial. It's really a turntable/tonearm/cart mechanical issue, the electronic effects of which you're treating with a subsonic filter.

    Of course, go ahead and use a phono pre with a subsonic filter to make your system playable. It works OK and people have been doing that for decades, it's perfectly common. But you may want to keep your eye out now and for the future for some kind of different mechanical improvements to your record playing set up.
     
    rocketmotor, Kyhl, patient_ot and 2 others like this.
  18. branden_8091

    branden_8091 New Member Thread Starter

    Location:
    Ontario, Canada
    Got you. Thanks for the detailed explanation! My TT is not old, and compliance must be good because it has the stock Ortofon 2M cart. I've just upgraded the stylus. But it seems that having an entry level turntable such as this, with speakers which cost 3x as much as it is the problem. They're reproducing the imperfections in my turntable. I guess it'll be time to go shopping once I can afford a better one, with a more isolated motor and better bearings :)
     
  19. Ken Clark

    Ken Clark Forum Resident

    Location:
    Chicago Suburbs
    The KAB filter may be a "band-aid", but it's a really good one. My woofers pumped even at very moderate volume and I don't have the flexibility to move equipment or speakers around. I bought the KAB and the issue is completely resolved. I can discern absolutely no audible difference.
     
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  20. patient_ot

    patient_ot Forum Resident

    Location:
    USA
    The design of most of the low-end Pro-Jects are not good IMHO. I've handled them, listened to them, and looked at them. The motor mount situation and the flyweight arm in particular are likely issues with this TT leading to enhanced subsonic rumble that you would not hear on better designs or even some vintage decks. Unfortunately too many companies these days are making these rubber band TTs that are really nothing more than an off-the-shelf industrial motor strapped to a piece of particle board/MDF.
     
  21. Boltman92124

    Boltman92124 Fish tacos

    Location:
    San Diego
    Nothing unusual about needing a 20hz low pass filter with vinyl. It doesn't mean there's something wrong with your system. I have one engaged on my power amp. Doesn't effect the sound at all.
     
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  22. Kyhl

    Kyhl formerly known

    Location:
    Savage
    From what I could put together using VinylEngine's resonance calculator, the combo would have about an 8hz resonance frequency.
    Used:
    Arm 11g
    Cart 7.2g
    Fasteners 1g Note, more weight would lower the resonance frequency
    Cart Compliance listed as 20. Don't know if that is dynamic, static, 10hz, or 100hz. Assuming it is 20 dynamic @ 10hz puts the resonance at 8hz, which is low and fits the description of the OP.

    Adding more mass to the assembly will make things worse. A cart with lower compliance rating seems to be the solution.
     
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  23. patient_ot

    patient_ot Forum Resident

    Location:
    USA
    IIRC the Debut Carbon arm is more like 6g effective mass. And yes the Ortofon compliance specs are dynamic @10hz.

    To confirm you can use a test record with tonearm resonance tests and software, or a record of actual music and software.
     
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  24. Kyhl

    Kyhl formerly known

    Location:
    Savage
    I saw something claiming 6g too, so maybe. You are right though. I used numbers for the 9" arm. Looks like the Debut uses a shorter arm to lower the mass. They list it at 9.5, not 11.

    Revising using 9.5 raises the resonence frequency to 8.5 hz. 6g would be closer at 9.5 hz. If it is possible to really get the arm that low.
     
  25. patient_ot

    patient_ot Forum Resident

    Location:
    USA
    Right off the site, specs below:

    Speed 33.45 (manual speed change)
    Drive principle belt drive
    Platter 300mm metal with felt mat
    Mains bearing stainless steel
    Wow & flutter 33: +/- 0.60%, 45: +/- 0.70%
    Speed drift 33: +/- 0.19%, 45: +/- 0.17%
    Signal to noise 68dB
    Tonearm 8.6”, Carbon
    Effective arm length 218.5 mm
    Effective arm mass 6.0 g
    Overhang 18.5mm
     

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